摘要:

The frequency dispersion in the complex dynamic modulus functions of polyethylene terephthalate and its related polymers over a frequency range from 0.05 to 50 cps was measured at various temperatures from −170° to 200°C covering the secondary glass transition, primary glass transition, and crystal disordering temperatures of these polymers.

ISSN:0022-2348    

DOI:10.1080/00222347008212471

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

It is known that trans-1,4-polybutadiene shows a crystal transformation at about 76°C. The crystal structure of the high-temperature form of trans-1,4-polybutadiene has been studied by X-ray diffraction. The chain conformation of the high-temperature form is similar to that of the low-temperature form. Above the crystal transformation temperature, the CH2─CH2bond remains trans, but the internal rotation angles around two CH2─CH bonds are decreased to 80° and −80° from 109° and −109°, respectively. The molecular chains, however, are considered to be in a considerably distorted state due to torsional oscillation about the C─C bonds. It is shown that the X-ray diffraction pattern of the high-temperature form can be explained by taking into account the rotational motion of the chain segments around the molecular axes.

ISSN:0022-2348    

DOI:10.1080/00222347008212472

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The Maron theory of polymer solutions was used to examine the 30°C vapor pressure data of Tait and Livesey on solutions of polyheptene-1, polydecene-1, polydodecene-1, and polyoctadecene-1 in toluene. For polyheptene-1 and polydecene-1, excellent agreement was obtained between theory and experiment over the entire concentration range studied. However, for the other two polymers, deviations were observed between the calculated and observed vapor pressures at higher solution concentrations. These deviations were used to show the presence of crystallinity in these and to ascertain the amounts. Further, it was shown that only one crystalline form of the polymer was present in the polydodecene-1, whereas in the polyoctadecene-1 two crystalline forms were detected. These observations, confirmed by measurements with a differential thermal analyzer (DTA), indicate that for polydodecene-1 and one of the crystalline forms in polyoctadecene-1 the crystallization involves alignment of both backbone and side chains; however, the lower melting form in polyoctadecene-1 appears to have only the side chains aligned in the crystal lattice.

ISSN:0022-2348    

DOI:10.1080/00222347008212473

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

In the course of systematic study of the solid-state polymerization of the cyclic oligomers of formaldehyde (─CH2─O─)m, it was found that pentoxane (─CH2─O─)5undergoes polymerization in the solid state to form polyoxymethylene (─CH2─O─)nby X-irradiation. The present article contains (a) the molecular and crystal structure determination of pentoxane, (b) the determination of the relative crystal orientation of pentoxane and the resultant polyoxymethylene, and (c) some discussions on the role played by the crystal structure of pentoxane in the solid state polymerization comparing with the cases of trioxane and tetraoxane.

ISSN:0022-2348    

DOI:10.1080/00222347008212474

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Moiré lines of bilayered polyethylene single crystals, superposed with slightly different orientation, changed their spacing and orientation locally in limited regions of several thousand angstroms when annealed at temperatures higher than their crystallization temperature. A pair of terminating moiré half-lines with opposite signs were found around these regions. The edge dislocation density was measured at various annealing temperatures as a function of time. On the basis of the results, a mechanism of generation of the edge dislocations is presented. During annealing, lattice planes in the limited regions of the bilayered crystals are sheared in a direction that reduces the orientational mismatch angle. In the domain of the sheared region the two lamellae come in close contact to form a network of screw dislocations between them. Edge dislocations are generated at the boundary of the sheared region. The size of the sheared region can be evaluated thermodynamically provided that the free energy of formation of the sheared region is minimized. Observed sizes of the sheared regions were found to be comparable with the calculated values. The fact that the images of the moiré lines of the as-grown crystals, kept for a prolonged time at the crystallization temperature in their mother liquor, were frequently changed into those of the screw dislocations or the moiré lines similar to those found in the annealed crystals is interpreted by the same theoretical considerations.

ISSN:0022-2348    

DOI:10.1080/00222347008212475

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The relative merits of time-temperature superposition procedures (those of Leaderman, Tobolsky, Ferry, Kě, McCrum, and Morris) have been assessed for the glass-rubber (a) relaxation of an epoxy resin. Measurements of creep compliance in shear were made at temperatures between 24° and 190°C. The different superposition procedures yield shift factor versus temperature plots which are essentially identical. Differences between the procedures are greatest in the master curves particularly at short and at long times. The McCrum-Morris procedure alone yielded a smooth master curve at all times. At temperatures above the glass transition the shift factor versus temperature plots followed the WLF equation.

ISSN:0022-2348    

DOI:10.1080/00222347008212476

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

This is the third article in a series dealing with the mechanical behavior of a system of fibrils, capable of a phase change, embedded in a matrix. The fibrils are characterized by a “critical” stress fcwhich is required to initiate the formation of the secondary phase B from the primary phase A, and a lower “equilibrium” stress fenecessary to maintain the thermodynamic equilibrium between the two phases. The effects of possible slip at the interface between fibril and matrix are calculated. The results are shown to be also applicable to a system of continuous or discontinuous fracturing fibrils in a matrix.

ISSN:0022-2348    

DOI:10.1080/00222347008212477

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The plastic deformation of polybutene-1 crystals on a uniaxially drawn substrate has been studied using an electron microscope. Crystals with hexagonal morphology and crystal structure, with orthorhombic structure and with square morphology were investigated. In all cases cracks spanned by fibrils were evident; for the crystals with the orthorhombic structure, shear-induced kinking and buckling also occurred.

ISSN:0022-2348    

DOI:10.1080/00222347008212478

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Stress-relaxation measurements have been conducted over the temperature range 15°–105°C on mats of single crystals of two linear polyethylene fractions. The single crystals were grown isothermally at several different temperatures. The relaxation modulus was observed to be strain dependent, indicating that the single crystal mats exhibited nonlinearity.

ISSN:0022-2348    

DOI:10.1080/00222347008212479

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The minimum energy conformations of some isolated and multi-molecular structures of poly-(gly-pro-gly) have been calculated and are presented. The poly-L-proline II helix is not among the four most stable isolated strand conformations, which are numbered here RM 1-4. It is shown that only one of these structures (RM 4) can pack efficiently into a stable crystal form. However, a sacrifice in intramolecular stabilization energy can be recovered in intermolecular interaction for the polyproline II-type conformation. A consideration of these factors leads to at least three possible crystal structures of comparable lattice energy. Each of the structures has an orthogonal unit cell and is sheetlike, but is distinguishable from the others either by chain conformation or packing arrangement. Two of the three structures are compatible with the X-ray evidence for poly-(gly-pro-gly) crystals precipitated from formic acid.

ISSN:0022-2348    

DOI:10.1080/00222347008212480

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor